Apologeticae sive Theologiae Fundamentalis, Tomus II (Pars Altera): Demonstratio Catholica

"Sanctity is said to be that by which the mind of man applies itself and its acts to God."¹ The Church, therefore, in order to be efficaciously holy, must apply the minds and acts of the faithful to God, i. e. it must conform their external and internal life to the divine will by fleeing sins and cultivating virtues. That the true Church is distinguished from the false by this holiness is made indubitable from the words of the Savior: "By their fruits you will know them … Every good tree bears good fruits: but the evil tree bears evil fruits."² A good tree has a fruit-bearing nature, exercises a fruit-bearing power, and actually bears good fruits. So too the Church of Christ should excel in holiness of doctrine, of means, and of members.

1. By holiness of doctrine. For Christ, holiness itself, without doubt preached a holy doctrine, i. e. such a one as impels men to moral holiness and shows them the way of perfection: "Be you therefore perfect, as also your heavenly Father is perfect."³ Hence also the Church of Christ obliges and leads men to holiness. But if any religious society does not form men to holiness, and much more, if it makes little of external good works or of the internal perfection of mind and heart, it cannot be the true Church of Christ.

2. By holiness of means. Christ, since He does not command impossibilities, also provided helps by which weak men might attain holiness: "As many as received him, he gave them power to become sons of God;"⁴ "Christ loved the Church and delivered himself up for her, that he might sanctify her;"⁵ "He gave himself for us, that he might redeem us from all iniquity and cleanse for himself an acceptable people, a pursuer of good works."⁶ Therefore also the Church of Christ should take care to provide all those effective means and helps which are necessary, useful, and suitable for attaining holiness. But if a religious group cares little about these means or utterly neglects them, it is not the Church of Christ.

3. By holiness of members. Not indeed all members of the Church are holy. For we have already shown that sinners too are found in her. Nevertheless, besides sinners, holy members also always exist in her. For if there are tares in the field, the wheat is present at the same time; if in the banquet a man appears lacking the wedding garment, others are seen clothed with this garment; in the net, besides bad fish, good ones also are found; together with the foolish virgins, the prudent ones are also beheld. And although sometimes the wicked may be more numerous than the good in the Church, nevertheless, because the denomination is taken from the better and sounder part, the Church can be called holy without qualification. The apostles themselves therefore call Christians saints, because all are destined for holiness and at least many of them are truly holy. Thus Paul writes "to all that are at Rome, beloved of God, called saints"⁷; "to the Church of God that is at Corinth, sanctified in Christ Jesus"⁸; "to all the saints who are at Ephesus".⁹ From all these things we gather with certainty not only that holiness, simply so called, never fails the true Church, but we already further infer that holiness also, eminent or said with emphasis, always shines in her.